When a malignant tumor is found in a breast, generally treatment involves either mastectomy or lumpectomy, sometimes followed by radiation therapy. The location of the tumor is found by different imaging modalities, such as x-ray, ultrasound, CT, MRI and others. After locating the tumor, a portion of the tissue, including the cancerous portion and a layer of healthy tissue surrounding the cancerous portion, is excised. It is important that the layer of healthy tissue envelop (enclose) the cancerous portion, to ensure that all the malignancy has been removed. This layer is often referred to as a “clean margin”, and its depth or thickness may range from 1 cell layer, or about 40 microns, to 10 mm (or other values, depending on the tumor, location and other factors); often a few millimeters is considered a clean margin.
A pathologist samples the margins of the excised portion at different points, especially suspicious points, to assess whether or not the tissue margins around the outer surface of the excised lump are free of cancerous tissue. Currently, there are no real-time means to assess margin status (frozen sections done for determining axillary lymph node involvement cannot be done on breast tissue due to high fat content), and standard pathologic evaluation of the excised lump can last a few days to weeks. If pathology results are positive, the patient needs to undergo another operation, until the cancerous tissue has been completely removed.